Composite bsi structure and method of manufacturing the same

ABSTRACT

Various embodiments of the present application are directed towards image sensors including composite backside illuminated (CBSI) structures to enhance performance. In some embodiments, a first trench isolation structure extends into a backside of a substrate to a first depth and comprises a pair of first trench isolation segments. A photodetector is in the substrate, between and bordering the first trench isolation segments. A second trench isolation structure is between the first trench isolation segments and extends into the backside of the substrate to a second depth less than the first depth. The second trench isolation structure comprises a pair of second trench isolation segments. An absorption enhancement structure overlies the photodetector, between the second trench isolation segments, and is recessed into the backside of the semiconductor substrate. The absorption enhancement structure and the second trench isolation structure collectively define a CBSI structure.

REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of U.S. application Ser. No.16/521,876, filed on Jul. 25, 2019, which claims the benefit of U.S.Provisional Application No. 62/764,964, filed on Aug. 15, 2018. Thecontents of the above-referenced Patent Applications are herebyincorporated by reference in their entirety.

BACKGROUND

Integrated circuits (ICs) with image sensors are used in a wide range ofmodern-day electronic devices, such as, for example, cameras and cellphones. In recent years, complementary metal-oxide semiconductor (CMOS)image sensors have begun to see widespread use, largely replacingcharge-coupled device (CCD) image sensors. Compared to CCD imagesensors, CMOS image sensors are favored due to low power consumption,small size, fast data processing, a direct output of data, and lowmanufacturing cost. One type of CMOS image sensor is a backsideilluminated (BSI) CMOS image sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A and 1B illustrate cross-sectional views of various embodimentsof image sensors comprising composite backside illuminated (CBSI)structures to enhance performance.

FIGS. 2A-2D illustrate top layouts of various embodiments of a CBSIstructure in FIGS. 1A and 1B.

FIGS. 3A and 3B illustrate cross-sectional views of some alternativeembodiments of the image sensors of FIGS. 1A and 1B in which the imagesensors comprise composite grids.

FIGS. 4A and 4B illustrate cross-sectional views of some alternativeembodiments of the image sensors of FIGS. 1A and 1B in which intra-pixeltrench isolation structures adjoin, and are offset from outer edges of,absorption enhancement structures.

FIG. 5 illustrates a top layout of some embodiments of a CBSI structurein FIGS. 4A and 4B.

FIGS. 6A and 6B illustrate cross-sectional views of some alternativeembodiments of the image sensors of FIGS. 4A and 4B in which the imagesensors comprise composite grids.

FIG. 7 illustrates a cross-sectional view of some alternativeembodiments of the image sensor of FIG. 1A in which intra-pixel trenchisolation structures are spaced from absorption enhancement structures.

FIG. 8 illustrates a top layout of some embodiments of a CBSI structurein FIG. 7.

FIG. 9 illustrates a cross-sectional view of some alternativeembodiments of the image sensor of FIG. 7 in which the absorptionenhancement structures each comprise multiple protrusions.

FIG. 10 illustrates a cross-sectional view of some alternativeembodiments of the image sensor of FIG. 7 in which the image sensorcomprises a composite grid.

FIGS. 11A and 11B illustrate cross-sectional views of variousalternative embodiments of the image sensor of FIG. 1A in whichintra-pixel trench isolation structures have columnar profiles and arelocalized to centers of absorption enhancement structures.

FIG. 12 illustrates a top layout of some embodiments of a CBSI structurein FIGS. 11A and 11B.

FIG. 13 illustrates a cross-sectional view of some alternativeembodiments of the image sensor of FIG. 11A in which the CBSI structureseach comprise multiple absorption enhancement structures and multipleintra-pixel trench isolation structures.

FIGS. 14A and 14B illustrate cross-sectional views of some alternativeembodiments of the image sensors of FIGS. 11A and 11B in which the imagesensors comprise composite grids.

FIG. 15 illustrates a cross-sectional view of some embodiments of a 3DBSI image sensor comprising CBSI structures to enhance performance.

FIGS. 16-20 illustrate cross-sectional views of some embodiments of amethod for forming an image sensor comprising CBSI structures.

FIG. 21 illustrates a block diagram of some embodiments of the method ofFIGS. 16-20.

FIGS. 22-28 illustrate cross-sectional views of some alternativeembodiments of a method for forming an image sensor comprising CBSIstructures in which the image sensor further comprises a composite grid.

FIG. 29 illustrates a block diagram of some embodiments of the method ofFIGS. 22-28.

FIGS. 30-46 illustrate cross-sectional views of some embodiments of amethod for forming a 3D BSI image sensor comprising CBSI structures toenhance performance.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

A complementary metal-oxide-semiconductor (CMOS) image sensor comprisesa semiconductor substrate, and further comprises an array of pixelsensors in the semiconductor substrate. The pixel sensors compriserespective photodetectors buried in the semiconductor substrate, andfurther comprise respective pixel transistors arranged on a surface ofthe semiconductor substrate. The photodetectors are configured to absorbincident radiation and to generate an electric signal corresponding tothe incident radiation.

Often, but not always, the semiconductor substrate is or comprisesmonocrystalline silicon due to the low cost and pervasiveness ofmonocrystalline silicon wafers in the semiconductor industry. However,monocrystalline silicon has a low absorption coefficient for highwavelength radiation, which includes, but is not limited to, nearinfrared radiation (NIR) and infrared radiation. As a result, thephotodetectors have low quantum efficiency for high wavelengthradiations and the CMOS image sensor may be unsuitable for use with highwavelength radiation. Additionally, the semiconductor industrycontinuously strives to reduce pixel pitch and increase pixel density.However, as pixel pitch decreases, optical performance degrades sincethe pixel sensors have reduced area for absorption of radiation.Therefore, the semiconductor industry is trending in a direction thatexacerbates the challenges associated with the CMOS image sensor basedon monocrystalline silicon.

Various embodiments of the present application are directed to an imagesensor comprising a plurality of pixel sensors with composite backsideilluminated (CBSI) structures for enhanced performance. In someembodiments, the image sensor comprises a substrate, a first trenchisolation structure, a photodetector, a second trench isolationstructure, and an absorption enhancement structure. The first trenchisolation structure extends into a backside of a substrate to a firstdepth and comprises a pair of first trench isolation segments. Thephotodetector is in the substrate, between and bordering the firsttrench isolation segments. The second trench isolation structure isbetween the first trench isolation segments and extends into thebackside of the substrate to a second depth less than the first depth.The second trench isolation structure comprises a pair of second trenchisolation segments. An absorption enhancement structure overlies thephotodetector, between the second trench isolation segments, and isrecessed into the backside of the semiconductor substrate. Theabsorption enhancement structure and the second trench isolationstructure collectively define a CBSI structure.

The CBSI structure allows radiation to enter the substrate unimpeded andserves as a reflector for the radiation once the radiation has enteredthe substrate. This may, for example, be achieved by total internalreflection (TIR) in embodiments in which the CBSI structure is orcomprises a material with a refractive index less than that of thesubstrate. By reflecting the radiation, the second trench isolationstructure prevents the radiation from passing from the photodetector toa neighboring photodetector and hence reduces crosstalk. Further, thesecond trench isolation structure reflects the radiation back to thephotodetector and hence increases absorption of the radiation. Theabsorption enhancement structure similarly reflects the radiation backto the photodetector and hence increase absorption of the radiation.However, the absorption enhancement structure is focused on portions ofthe radiation that have passed through the substrate unabsorbed and havebeen reflected back towards the backside of the substrate (e.g., by anunderlying interconnect structure). Angled sidewalls of the absorptionenhancement structure may, for example, increase the likelihood of TIR,thereby enhancing reflectance and increasing the amount of radiationreflected to the photodetector.

With reference to FIG. 1A, a cross-sectional view 100A of someembodiments of an image sensor comprising CBSI structures 102 forimproved image performance is provided. The image sensor may, forexample, be a backside illuminated (BSI) CMOS image sensor or some othersuitable image sensor. Multiple pixel sensors 104 are on a frontside 106f of a semiconductor substrate 106, and the pixel sensors 104 compriseindividual photodetectors 108 in the semiconductor substrate 106. Thesemiconductor substrate 106 may be or comprise, for example, a bulksilicon substrate, a silicon-on-insulator (SOI) substrate, or some othersuitable semiconductor substrate. The pixel sensors 104 may be, forexample, active pixel sensors (APSs) or some other suitable pixelsensors, and the photodetectors 108 may, for example, be or comprisephotodiodes or some other suitable photodetectors. In some embodiments,a pitch P of the pixel sensors 104 is about 0.5-4.4 micrometers, about0.4-2.45 micrometers, or about 2.45-4.4 micrometers. In someembodiments, a width W_(p) of the pixel sensors 104 is about 0.8micrometers, 0.9 micrometers, 1 micrometer, 1.1 micrometers, or about0.8-1.1 micrometers. Other pitches and/or widths are, however, amenablefor the pixel sensors 104.

The CBSI structures 102 are individual to the pixel sensors 104 andoverlie the pixel sensors 104 on a backside 106 b of the semiconductorsubstrate 106. Further, the CBSI structures 102 are part of a backsidedielectric layer 110 on the backside 106 b of the semiconductorsubstrate 106 and comprise individual absorption enhancement structures112 and individual intra-pixel trench isolation structures 114. Forillustrative purposes, the hashing has been varied between theabsorption enhancement structures 112, the intra-pixel trench isolationstructures 114, and a remainder of the backside dielectric layer 110.Notwithstanding the change in hashing, it should be appreciated that theabsorption enhancement structures 112 and the intra-pixel trenchisolation structures 114 are still part of the backside dielectric layer110. The backside dielectric layer 110 may be or comprise, for example,silicon oxide, a high k dielectric, some other suitable dielectric(s),or any combination of the foregoing. A high k dielectric may, forexample, be a dielectric with a dielectric constant greater than about3.9, 10, or 20.

The absorption enhancement structures 112 protrude into the backside 106b of the semiconductor substrate 106 and have angled sidewalls. In someembodiments, the absorption enhancement structures 112 adjoin thephotodetectors 108 and/or have bottom profiles that are triangular.Other bottom profiles are, however, amenable. The intra-pixel trenchisolation structures 114 adjoin the absorption enhancement structures112 and protrude into the backside 106 b of the semiconductor substrate106 to a first depth D₁. The first depth D₁ may, for example, be orcomprise 0.1-3.0 micrometers, about 0.10-1.55 micrometers, about1.55-3.0 micrometers, about 0.5 micrometers, or about 0.55 micrometers.Other suitable values are, however, amenable for the first depth D₁. Theintra-pixel trench isolation structures 114 comprise individual pairs ofintra-pixel trench isolation segments (not individually labeled), andthe absorption enhancement structures 112 are between the intra-pixeltrench isolation segments of corresponding pairs.

An inter-pixel trench isolation structure 116 separates the pixelsensors 104 from each other and is part of the backside dielectric layer110. Further, the inter-pixel trench isolation structure 116 protrudesinto the backside 106 b of the semiconductor substrate 106 to a seconddepth D₂. The second depth D₂ is greater than the first depth D₁ andmay, for example, be about 1-5 micrometers, about 1-3 micrometers, about3-5 micrometers, about 1.5 micrometers, or about 2 micrometers. Othersuitable values are, however, amenable for the second depth D₂.

During operation of the image sensor, the image sensor receivesradiation 118 from the backside 106 b of the semiconductor substrate106. The radiation 118 may, for example, be or comprise high wavelengthradiation or other suitable radiation. The high wavelength radiationincludes 850 nanometer radiation and 940 nanometer radiation(collectively NIR radiation) and/or radiation with wavelengths in excessof about 850 or 940 nanometers. The radiation 118 impinges on and isabsorbed by the photodetectors 108, thereby generating electricalsignals that allow imaging. The CBSI structures 102 and the inter-pixeltrench isolation structure 116 reduce cross talk between the pixelsensors 104 and increase absorption of the radiation 118, therebyenhancing quantum efficiency and performance of the image sensor.Supposing the width W_(p) of the pixel sensors 104 is about onemicrometer, simulations indicate that the CBSI structures 102 may, forexample, enhance quantum efficiency by about 3.3% and about 0.3%respectively for 850 nanometer radiation and 940 nanometer radiationcompared to an image sensor without the intra-pixel trench isolationstructures 114.

The CBSI structures 102 allow the radiation 118 to enter thesemiconductor substrate 106 unimpeded and serve as reflectors for theradiation 118 once the radiation 118 has entered the semiconductorsubstrate 106. This may, for example, be achieved by TIR in embodimentsin which the CBSI structures 102 are or comprise a material with arefractive index less than that of the semiconductor substrate 106. Forexample, the CBSI structures 102 may be or comprise silicon oxide andthe semiconductor substrate 106 may be or comprise monocrystallinesilicon since silicon oxide has a refractive index less than that ofmonocrystalline silicon. Pursuant to Snell's Law, TIR occurs at the CBSIstructures 102 for portions of the radiation 118 traveling from thesemiconductor substrate 106 to the CBSI structures 102 but does notoccur for portions of the radiation 118 traveling from the CBSIstructures 102 to the semiconductor substrate 106.

By reflecting the radiation 118, the intra-pixel trench isolationstructures 114 prevent the radiation 118 from passing between the pixelsensors 104 and hence reduce crosstalk. Further, the intra-pixel trenchisolation structures 114 reflect the radiation 118 back to thephotodetectors 108 and hence increase absorption of the radiation 118.The absorption enhancement structures 112 similarly reflect theradiation 118 back to the photodetectors 108 and hence increaseabsorption of the radiation 118. However, the absorption enhancementstructures 112 are focused on portions of the radiation 118 that havepassed through the semiconductor substrate 106 unabsorbed and have beenreflected back towards the backside 106 b of the semiconductor substrate106 from an underlying interconnect structure (not shown). The slantedsidewalls of the absorption enhancement structures 112 may, for example,increase the likelihood of TIR for these portions of the radiation 118.

In some embodiments, the semiconductor substrate 106 comprises ananoporous layer 106 np along the backside 106 b of the semiconductorsubstrate 106 to further enhance absorption of the radiation 118. Thenanoporous layer 106 np has a comparatively high concentration ofnanopores relative to a remainder of the semiconductor substrate 106 andmay, for example, be or comprise nanoporous silicon or some othersuitable material. The high concentration of nanopores effectivelyreduces the bandgap of the nanoporous layer 106 np and hence increasesthe absorption coefficient of the semiconductor substrate 106 along thebackside 106 b of the semiconductor substrate 106 and at the absorptionenhancement structures 112.

Similar to the CBSI structures 102, the inter-pixel trench isolationstructure 116 serves as a reflector for the radiation 118. Reflectancemay, for example, be achieved by TIR in embodiments in which theinter-pixel trench isolation structure 116 is or comprise a materialwith a refractive index less than that of the semiconductor substrate106. Additionally, or alternatively, reflectance may be achieved by areflective material (e.g., metal or some other suitable reflectivematerial). By reflecting the radiation 118, the inter-pixel trenchisolation structure 116 prevents the radiation 118 from passing betweenthe pixel sensors 104 and hence reduces crosstalk. Further, theinter-pixel trench isolation structure 116 reflects the radiation 118back to the photodetectors 108 and hence increases absorption of theradiation 118.

In some embodiments, color filters 120 and/or microlenses 122 arestacked over the pixel sensors 104 and the backside dielectric layer110. For ease of illustration, only some of the color filters 120 arelabeled 120, and only some of the microlenses 122 are labeled 122. Thecolor filters 120 transmit assigned wavelengths of the radiation 118while blocking unassigned wavelengths of the radiation 118. For example,one of the color filters 120 may transmit red wavelengths of radiationwhile blocking blue wavelengths of radiation, whereas another one of thecolor filters 120 may transmit blue wavelengths of radiation whileblocking red wavelengths of radiation. The microlenses 122 focus theradiation 118 on the photodetectors 108 and hence enhance absorption ofthe radiation 118.

With reference to FIG. 1B, a cross-sectional view 100B of somealternative embodiments of the image sensor of FIG. 1A is provided inwhich in which bottom profiles of the absorption enhancement structures112 are flat. Other profiles are, however, amenable.

With reference to FIG. 2A, a top layout 200A of some embodiments of anyone of the CBSI structures 102 in FIGS. 1A and 1B is provided. Thecross-sectional view of the CBSI structure in FIGS. 1A and 1B may, forexample, be taken along line A. For clarity, the top layout 200Aillustrates the absorption enhancement structure 112 and the intra-pixeltrench isolation structure 114 separately and further illustrates acombination of the absorption enhancement structure 112 and theintra-pixel trench isolation structure 114. As should be appreciated,it's the combination that corresponds to the CBSI structure 102 in FIGS.1A and 1B.

The intra-pixel trench isolation structure 114 has a square ring-shapedlayout and the absorption enhancement structure 112 has a diamond shapedlayout. Other layouts are, however, amenable. In some embodiments, awidth W_(ti) of the intra-pixel trench isolation structure 114 is about0.05-1.00 micrometers, about 0.05-.50 micrometers, about 0.5-1.0micrometers, about 0.17 micrometers, or about 0.12 micrometers. In someembodiments, a width W_(ae) of the absorption enhancement structure 112is about 0.05-1.0 micrometers, about 0.05-.50 micrometers, about 0.5-1.0micrometers. Other suitable values are, however, amenable for the widthsW_(ti), W_(ae).

With reference to FIGS. 2B-2D, top layouts 200B-200D of variousalternative embodiments of the CBSI structure 102 of FIG. 2A isprovided. The intra-pixel trench isolation structure 114 has a diamondring-shaped layout in FIG. 2B, and the intra-pixel trench isolationstructure 114 has different cross shaped layouts in FIGS. 2C and 2D.Additional layouts are, however, amenable.

With reference to FIG. 3A, a cross-sectional view 300A of somealternative embodiments of the image sensor of FIG. 1A is provided inwhich the image sensor comprises a composite grid 302 on the backside106 b of the semiconductor substrate 106. The composite grid 302accommodates the color filters 120, and the microlenses 122 overlie thecolor filters 120 and the composite grid 302. The composite grid 302comprises a metal grid 304, a dielectric grid 306, and a hard mask grid308. In alternative embodiments, the hard mask grid 308 is omitted. Thedielectric grid 306 overlies the metal grid 304, and the hard mask grid308 overlies the dielectric grid 306.

A metal layer 312, a backside dielectric layer 314, and a hard masklayer 316 respectively define the metal grid 304, the dielectric grid306, and the hard mask grid 308. The metal layer 312 may, for example,be or comprise tungsten, aluminum copper, titanium nitride, some othersuitable metal(s), or any combination of the foregoing. In someembodiments, the metal layer 312 comprises a titanium nitride layer, andfurther comprises a tungsten layer overlying the titanium nitride layer.In alternative embodiments, the metal layer 312 comprises a top titaniumnitride layer and a bottom titanium nitride layer, and further comprisesan aluminum copper layer between the top and bottom titanium layers. Inalternative embodiments, the metal layer 312 comprises the top titaniumnitride layer and the aluminum copper layer, but not the bottom titaniumnitride layer. The backside dielectric layer 314 may be or comprise, forexample, silicon oxide and/or some other suitable dielectric(s). Thehard mask layer 316 may be or comprise, for example, silicon nitrideand/or some other suitable dielectric(s).

A first backside liner 318 and a second backside liner 320 line anunderside of the backside dielectric layer 314 and are arranged so thesecond backside liner 320 is between the first backside liner 318 andthe backside dielectric layer 314. Further, the first and secondbackside liners 318, 320 separate the backside dielectric layer 314 fromthe CBSI structures 102 and define the inter-pixel trench isolationstructure 116 with the backside dielectric layer 314. The first backsideliner 318 and/or the CBSI structures 102 may be or comprise, forexample, silicon oxide and/or some other suitable dielectric(s). In someembodiments, the first backside liner 318 and/or the CBSI structures 102are or comprise the same material and/or are portions of the samedeposition. The second backside liner 320 may be or comprise, forexample, hafnium oxide, tantalum oxide, some other suitable high kdielectric(s), or any combination of the foregoing.

With reference to FIG. 3B, a cross-sectional view 300B of somealternative embodiments of the image sensor of FIG. 3A is provided inwhich in which bottom profiles of the absorption enhancement structures112 are flat. Other profiles are, however, amenable.

With reference to FIGS. 4A and 4B, cross-sectional views 400A, 400B ofsome alternative embodiments of the image sensors of FIGS. 1A and 1B areprovided in which the intra-pixel trench isolation structures 114 adjointhe absorption enhancement structures 112 and are offset from outeredges of the absorption enhancement structures 112 by an offset O.Supposing the pixel sensors 104 have a width W_(p) of about onemicrometer, simulations indicate that the CBSI structures 102 may, forexample, enhance quantum efficiency by about 6.3% and about 2.8%respectively for 850 nanometer radiation and 940 nanometer radiationcompared to an image sensor without the intra-pixel trench isolationstructures 114.

With reference to FIG. 5, a top layout 500 of some embodiments of anyone of the CBSI structures 102 in FIGS. 4A and 4B is provided. Thecross-sectional view of the CBSI structure in FIGS. 4A and 4B may, forexample, be taken along line B. The top layout 500 is as the top layout200A of FIG. 2A is described, except for the offset O. Hence, theintra-pixel trench isolation structure 114 has a square ring-shapedlayout and the absorption enhancement structure 112 has a diamond shapedlayout. Other layouts are, however, amenable. For example, theintra-pixel trench isolation structure 114 may have a layout in any oneof FIGS. 2B-2D.

With reference to FIGS. 6A and 6B, cross-sectional views 600A, 600B ofsome alternative embodiments of the image sensors of FIGS. 4A and 4B areprovided in which the image sensors comprise composite grids 302 on thebacksides 106 b of the semiconductor substrates 106. The cross-sectionalviews 600A, 600B are as the cross-sectional views 300A, 300B of FIGS. 3Aand 3B are described, except for the offset O.

With reference to FIG. 7, a cross-sectional view 700 of some alternativeembodiments of the image sensor of FIG. 1A is provided in which theintra-pixel trench isolation structures 114 are spaced from theabsorption enhancement structures 112. Supposing the pixel sensors 104have a width W_(p) of about one micrometer, simulations indicate thatthe CBSI structures 102 may, for example, enhance quantum efficiency byabout 6.3% and about 2.8% respectively for 850 nanometer radiation and940 nanometer radiation compared to an image sensor without theintra-pixel trench isolation structures 114. As noted above with regardto FIG. 1A, the intra-pixel trench isolation structures 114 compriseindividual pairs of intra-pixel trench isolation segments (notindividually labeled). In alternative embodiments of the image sensor ofFIG. 7, edges of the intra-pixel trench isolation structures 114 adjoinedges of the absorption enhancement structures 112 while the absorptionenhancement structures 112 remain completely between the intra-pixeltrench isolation segments of corresponding pairs.

With reference to FIG. 8, a top layout 800 of some embodiments of anyone of the CBSI structures 102 in FIG. 7 is provided. Thecross-sectional view of the CBSI structure in FIG. 7 may, for example,be taken along line C. The top layout 800 is as the top layout 200A ofFIG. 2A is described, except that the absorption enhancement structure112 is spaced from the intra-pixel trench isolation structure 114.Hence, the intra-pixel trench isolation structure 114 has a squarering-shaped layout and the absorption enhancement structure 112 has adiamond shaped layout. Other layouts are, however, amenable. Forexample, the intra-pixel trench isolation structure 114 may have asquare ring shaped layout or some other suitable ring shaped layout thatcircumscribes the absorption enhancement structure 112.

With reference to FIG. 9, a cross-sectional view 900 of some alternativeembodiments of the image sensor of FIG. 7 is provided in which theabsorption enhancement structures 112 each have multiple protrusions.For example, as illustrated, the absorption enhancement structures 112each have two protrusions with triangular profiles. More than twoprotrusions and/or other protrusion profiles are, however, amenable.

With reference to FIG. 10, a cross-sectional view 1000 of somealternative embodiments of the image sensor of FIG. 7 is provided inwhich the image sensor comprises a composite grid 302 on the backside106 b of the semiconductor substrate 106. The cross-sectional view 900is as the cross-sectional views 300A, 300B of FIGS. 3A and 3B aredescribed, except that the intra-pixel trench isolation structures 114are spaced from the absorption enhancement structures 112. Inalternative embodiments, the absorption enhancement structures 112 eachhave multiple protrusions, an example of which is shown in FIG. 9.

With reference to FIG. 11A, a cross-sectional view 1100A of somealternative embodiments of the image sensor of FIG. 1A is provided inwhich the intra-pixel trench isolation structures 114 have columnarprofiles and are localized to centers of the absorption enhancementstructures 112. Other profiles are, however, amenable. Supposing thepixel sensors 104 have a width W_(p) of about one micrometer,simulations indicate that the CBSI structures 102 may, for example,enhance quantum efficiency by about 2.2% and about 0.8% respectively for850 nanometer radiation and 940 nanometer radiation compared to an imagesensor without the intra-pixel trench isolation structures 114.

With reference to FIG. 11B, a cross-sectional view 1100B of somealternative embodiments of the image sensor of FIG. 11A is provided inwhich a bottom profile of the intra-pixel trench isolation structures114 is triangular. Other profiles are, however, amenable. Slantedsidewalls at the bottom of the intra-pixel trench isolation structures114 may, for example, enhance TR in embodiments in which the intra-pixeltrench isolation structures 114 are or comprise a material with asmaller refractive index than that of the semiconductor substrate 106.As a result, radiation that has passed through the semiconductorsubstrate 106 unabsorbed and has been reflected back towards thebackside 106 b of the semiconductor substrate 106 from an underlyinginterconnect structure (not shown) is more likely to be reflected backto the photodetectors 108 by the intra-pixel trench isolation structures114. This, in turn, enhances quantum efficiency of the photodetectors108.

With reference to FIG. 12, a top layout 1200 of some embodiments of anyone of the CBSI structures 102 in FIGS. 11A and 11B is provided. Thecross-sectional view of the CBSI structure in FIGS. 11A and 11B may, forexample, be taken along line D. The top layout 1200 is as the top layout200A of FIG. 2A is described, except that the intra-pixel trenchisolation structure 114 has a square shaped layout and is localized to acenter of the absorption enhancement structure 112. Other layouts are,however, amenable. In some embodiments, increasing the width W_(ti) ofthe intra-pixel trench isolation structure 114 increases quantumefficiency at 850 nanometer radiation and/or 940 nanometer radiation.

With reference to FIG. 13, a cross-sectional view 1300 of somealternative embodiments of the image sensor of FIG. 11A is provided inwhich the CBSI structures 102 each comprise multiple absorptionenhancement structures 112 and multiple intra-pixel trench isolationstructures 114. For example, as illustrated, the CBSI structures 102each comprise two absorption enhancement structures 112 and twointra-pixel trench isolation structures 114. More than two absorptionenhancement structures 112 and/or more than two intra-pixel trenchisolation structures 114 are, however, amenable. The absorptionenhancement structures 112 and the intra-pixel trench isolationstructures 114 are paired, such that each pair has an absorptionenhancement structure and an intra-pixel trench isolation structure.Further, each pair is as a CBSI structure 102 of FIG. 11A and/or FIG. 12is illustrated and described.

While FIG. 13 is illustrated using embodiments of the intra-pixel trenchisolation structures 114 in FIG. 11A, embodiments of the intra-pixeltrench isolation structures 114 in FIG. 11B are also amenable. As such,it should be appreciated that bottom profiles of the intra-pixel trenchisolation structures 114 may alternatively be triangular as illustratedin FIG. 11B. Other bottom profiles are also amenable.

With reference to FIGS. 14A and 14B, cross-sectional views 1400A, 1400Bof some alternative embodiments of the image sensors of FIGS. 11A and11B are provided in which the image sensors comprise composite grids 302on the backsides 106 b of the semiconductor substrates 106. Thecross-sectional views 14A and 14B are as the cross-sectional views 300A,300B of FIGS. 3A and 3B are described, except that the intra-pixeltrench isolation structures 114 have columnar profiles and are localizedto centers of the absorption enhancement structures 112. Additionally,while FIGS. 14A and 14B illustrate the CBSI structures 102 as eachhaving a single intra-pixel trench isolation structure 114 and a singleabsorption enhancement structure 112, the CBSI structures 102 may eachhave two or more intra-pixel trench isolation structures 114 and two ormore absorption enhancement structures 112 in alternative embodiments.An example of such a configuration is illustrated and described withregard to FIG. 13.

With reference to FIG. 15, a cross-sectional view 1500 of someembodiments of a three-dimension (3D) BSI image sensor comprising CBSIstructures 102 is provided. The 3D BSI image sensor comprises a firstintegrated chip 1502 and a second integrated chip 1504 that are bondedtogether. The first integrated chip 1502 comprise a first substrate 106,a first interconnect structure 1506, and a plurality of transfertransistors 1508. For ease of illustration, only one of the transfertransistors 1508 is labeled 1508.

The first interconnect structure 1506 and the transfer transistors 1508are on a frontside of the first substrate 106, and the transfertransistors 1508 are between the first interconnect structure 1506 andthe first substrate 106. The first interconnect structure 1506 comprisesa first interconnect dielectric layer 1510, and further comprises aplurality of first wires 1512 and a plurality of first vias 1514. Forease of illustration, only some of the first wires 1512 are labeled 1512and only some of the first vias 1514 are labeled 1514. The first wires1512 and the first vias 1514 are conductive and are alternatinglystacked in the first interconnect dielectric layer 1510 to defineconductive paths. The transfer transistors 1508 comprise individualtransfer gate stacks 1516 and individual source/drain regions. Firstsource/drain regions of the transfer transistors 1508 are defined byphotodetectors 108 in the first substrate 106, and second source/drainregions of the transfer transistors 1508 are defined by floatingdiffusion (FD) regions 1518 in the first substrate 106. For ease ofillustration, only one of the transfer gate stacks 1516 is labeled 1516,only one of the photodetectors 108 is labeled 108, and only one of theFD regions 1518 is labeled 1518.

In some embodiments, a frontside isolation structure 1520 extends intothe first substrate 106. For ease of illustration, only one segment ofthe frontside isolation structure 1520 is labeled 1520. In someembodiments, the frontside isolation structure 1520 separates thetransfer transistors 1508 and/or adjoins a pad structure 1522. The padstructure 1522 is exposed by a pad opening 1524 and is surrounded by apad dielectric liner 1526 and a pad dielectric layer 1528. The frontsideisolation structure 1520 may be or comprise, for example, a shallowtrench isolation (STI) structure or some other suitable isolationstructure.

The second integrated chip 1504 comprise a second substrate 1529, asecond interconnect structure 1530, and a plurality of logic transistors1532. For ease of illustration, only some of the logic transistors 1532are labeled 1532. The second integrated chip 1504 is bonded to the firstintegrated chip 1502, such that the first and second interconnectstructures 1506, 1530 are between the first and second substrate 106,1529. The second integrated chip 1504 may, for example, comprise imagesignal processing (ISP) circuitry, read and/or write circuitry, or someother suitable circuitry for readout of the photodetectors 108.

The second interconnect structure 1530 and the logic transistors 1532are on a frontside of the second substrate 1529, and the logictransistors 1532 are between the second interconnect structure 1530 andthe second substrate 1529. The second interconnect structure 1530comprises a second interconnect dielectric layer 1534, and furthercomprises a plurality of second wires 1536 and a plurality of secondvias 1538. For ease of illustration, only some of the second wires 1536are labeled 1536 and only some of the second vias 1538 are labeled 1538.The second wires 1536 and the second vias 1538 are conductive and arealternatingly stacked in the second interconnect dielectric layer 1534to define conductive paths.

CBSI structures 102 and an inter-pixel trench isolation structure 116extend into a backside of the first substrate 106. The CBSI structures102 overlie the photodetectors 108, and the inter-pixel trench isolationstructure 116 separates the photodetectors 108. For ease ofillustration, only one of three illustrated segments of the inter-pixeltrench isolation structure 116 are labeled 116. The CBSI structures 102and the inter-pixel trench isolation structure 116 may, for example, beas illustrated and described with regard to any one of the precedingfigures. (e.g., FIG. 1A or 6B). The inter-pixel trench isolationstructure 116 is defined by a first backside liner 318, a pair of secondbackside liners 320 a, 320 b, a third backside liner 1540, and a firstmetal grid 1542. In some embodiments, the CBSI structures 102 aredefined by the first backside liner 318, the pair of second backsideliners 320 a, 320 b, the third backside liner 1540, or any combinationof the foregoing. In alternative embodiments, the CBSI structures 102are independent of these liners 318, 320 a, 320 b, 1540. The first andthird backside liners 318, 1540 may be or comprise, for example, siliconoxide and/or some other suitable dielectric(s), and/or the secondbackside liners 320 a, 320 b may be or comprise, for example, high kdielectric(s) and/or some other suitable dielectric(s).

A cap layer 1544 covers the first metal grid 1542, and an etch stoplayer 1546, a metal layer 312, a backside dielectric layer 314 b, and ahard mask layer 316 are stacked over the cap layer 1544. The cap layer1544 may, for example, be or comprise silicon oxide and/or some othersuitable dielectric(s), and/or the etch stop layer 1546 may, forexample, be or comprise silicon nitride and/or some other suitabledielectric(s). The metal layer 312, the backside dielectric layer 314 b,and the hard mask layer 316 define a second metal grid 304, a dielectricgrid 306, and a hard mask grid 308 (collectively a composite grid 302).Further, the metal layer 312 defines protrusions 1548 extending into thefirst substrate 106. For ease of illustration, only one of twoillustrated protrusions 1548 is labeled 1548.

A composite grid liner 314 c lines the composite grid 302, and colorfilters 120 are recessed into the composite grid 302 over the compositegrid liner 314 c. Further microlenses 122 overlie the color filters 120.A through substrate via (TSV) 1550 protrudes through the first substrate106 and the first interconnect structure 1506 to the second interconnectstructure 1530 and is surrounded by a pair of TSV liners 1552, 1554 atthe first substrate 106. A first TSV liner 1552 of the pair may, forexample, be or comprise silicon oxide and/or some other suitabledielectric(s), whereas a second TSV liner 1554 of the pair may, forexample, be or comprise silicon nitride and/or some other suitabledielectric(s).

While FIG. 15 is illustrated using embodiments of the CBSI structures102 in FIG. 1A, it is to be appreciated that embodiments of the CBSIstructures 102 in any one of the preceding figures are amenable inalternative embodiments. For example, the 3D BSI image sensor of FIG. 15may alternatively have embodiments of the CBSI structures 102 in FIG. 1Bor 7.

With reference to FIGS. 16-20, a series of cross-sectional views1600-2000 of some embodiments of a method for forming an image sensorcomprising CBSI structures is provided. The cross-sectional views1600-2000 illustrate the method using the image sensor of FIG. 1A butmay also be used to form the image sensor in any one of FIGS. 1B, 4A,4B, 7, 9, 11A, 11B, and 13.

As illustrated by the cross-sectional view 1600 of FIG. 16, pixelsensors 104 are formed on a frontside 106 f of a semiconductor substrate106 and, in some embodiments, the semiconductor substrate 106 issubsequently thinned to reduce a thickness T_(ss) of the semiconductorsubstrate 106. The pixel sensors 104 comprise individual photodetectors108 in the semiconductor substrate 106 and, in some embodiments, furthercomprise individual transistors (not shown) on the frontside 106 f ofthe semiconductor substrate 106. The transistors may, for example, beused for readout of the photodetectors 108 and/or may, for example,comprise transfer transistors, reset transistors, select transistors,source follower transistors, some other suitable transistors, or anycombination of the foregoing. The thickness T_(ss) may, for example, beabout 3.0-4.0 micrometers, about 3.5-4.0 micrometers, or about 3.5-4.0micrometers upon completion of the thinning. Other thicknesses are,however, amenable.

Also illustrated by the cross-sectional view 1600 of FIG. 16, a backside106 b of the semiconductor substrate 106 is patterned to form absorptionenhancement openings 1602. The absorption enhancement openings 1602 areindividual to and respectively overlie the pixel sensors 104. Theabsorption enhancement openings 1602 are formed with a triangularprofile, but other profiles are amenable. For example, the absorptionenhancement openings 1602 may be formed with a profile matching theabsorption enhancement structures 112 in any one of FIGS. 1A, 1B, 7, 9,11A, 11B, or 13 and/or with a top layout matching the absorptionenhancement structure 112 in any one of FIGS. 2A-2D, 5, 8, and 12.

In some embodiments, the patterning is performed by an etching processor some other suitable patterning process. The etching process may, forexample, comprise: 1) forming a mask 1604 on the backside 106 b of thesemiconductor substrate 106; 2) applying one or more etchants 1606 tothe backside 106 b with the mask 1604 in place; and 3) stripping themask 1604. The mask 1604 may be or comprise, for example, photoresist,silicon nitride, some other suitable mask material, or any combinationof the foregoing.

As illustrated by the cross-sectional view 1700 of FIG. 17, the backside106 b of the semiconductor substrate 106 is further patterned to formintra-pixel isolation trenches 1702. The intra-pixel isolation trenches1702 are individual to the pixel sensors 104 and border and/or overlapthe absorption enhancement openings 1602 (see FIG. 16). The intra-pixelisolation trenches 1702 may be formed with a profile matching theintra-pixel trench isolation structures 114 in any one of FIGS. 1A, 1B,7, 9, 11A, 11B, or 13 and/or with a top layout matching the intra-pixeltrench isolation structure 114 in any one of FIGS. 2A-2D, 5, 8, and 12.In alternative embodiments, the intra-pixel isolation trenches 1702 areformed before the absorption enhancement openings 1602 (see FIG. 16) areformed.

In some embodiments, the patterning is performed by an etching processor some other suitable patterning process. The etching process may, forexample, comprise: 1) forming a mask 1704 on the backside 106 b of thesemiconductor substrate 106; 2) applying one or more etchants 1706 tothe backside 106 b with the mask 1704 in place; and 3) stripping themask 1704. The mask 1704 may be or comprise, for example, photoresist,silicon nitride, some other suitable mask material, or any combinationof the foregoing.

As illustrated by the cross-sectional view 1800 of FIG. 18, the backside106 b of the semiconductor substrate 106 is further patterned to form aninter-pixel isolation trench 1802. The inter-pixel isolation trench 1802separates the pixel sensors 104 from each other and may, for example,have a grid-shaped top layout or some other suitable top layout.

In some embodiments, the patterning is performed by an etching processor some other suitable patterning process. The etching process may, forexample, comprise: 1) forming a mask 1804 on the backside 106 b of thesemiconductor substrate 106; 2) applying one or more etchants 1806 tothe backside 106 b with the mask 1804 in place; and 3) stripping themask 1804. The mask 1804 may be or comprise, for example, photoresist,silicon nitride, silicon oxide, some other suitable mask material, orany combination of the foregoing, and/or the stripping may, for example,be performed by a tetramethylammonium hydroxide (TMAH) etchant and/orsome other suitable etchant(s).

As illustrated by the cross-sectional view 1900 of FIG. 19, a backsidedielectric layer 110 is formed covering the backside 106 b of thesemiconductor substrate 106, and further filling the inter-pixelisolation trench 1802 (see FIG. 18), the intra-pixel isolation trenches1702 (see FIG. 17), and the absorption enhancement openings 1602 (seeFIG. 16). The backside dielectric layer 110 defines CBSI structures 102in the intra-pixel isolation trenches 1702 and the absorptionenhancement openings 1602, and further defines an inter-pixel trenchisolation structure 116 in the inter-pixel isolation trench 1802. Thebackside dielectric layer 110 may be or comprise, for example, siliconoxide, a high k dielectric, some other suitable dielectric(s), or anycombination of the foregoing. In some embodiments, the backsidedielectric layer 110 is or comprises a material with a refractive indexless than that of the semiconductor substrate 106 to promote TIR.

In some embodiments for forming of the backside dielectric layer 110comprises: 1) depositing the backside dielectric layer 110; and 2)performing a planarization into an upper or top surface of the backsidedielectric layer 110. The deposition may, for example, be performed bychemical vapor deposition (CVD), physical vapor deposition (PVD),sputtering, thermal oxidation, some other suitable depositionprocess(es), or any combination of the foregoing. The planarization may,for example, be performed by a chemical mechanical polish (CMP) and/orsome other suitable planarization process(es).

As illustrated by the cross-sectional view 2000 of FIG. 20, colorfilters 120 and microlenses 122 are formed stacked on the backsidedielectric layer 110. For ease of illustration, only some of the colorfilters 120 are labeled 120 and only some of the microlenses 122 arelabeled 122.

Although the cross-sectional views 1600-2000 shown in FIGS. 16-20 aredescribed with reference to a method, it will be appreciated that thestructures shown in FIGS. 16-20 are not limited to the method but rathermay stand alone separate of the method. Although FIGS. 16-20 aredescribed as a series of acts, it will be appreciated that these actsare not limiting in that the order of the acts can be altered in otherembodiments, and the methods disclosed are also applicable to otherstructures. In other embodiments, some acts that are illustrated and/ordescribed may be omitted in whole or in part.

With reference to FIG. 21, a block diagram 2100 of some embodiments ofthe method of FIGS. 16-20 is provided.

At 2102, a substrate and a photodetector are provided, where thephotodetector is in the substrate. See, for example, FIG. 16.

At 2104, a first etch is performed into a backside of the substrate todefine an absorption enhancement opening with slanted sidewalls, wherethe opening overlies the photodetector. See, for example, FIG. 16.

At 2106, a second etch is performed into the backside of the substrateto define an intra-pixel isolation trench, where the intra-pixelisolation trench borders the absorption enhancement opening. See, forexample, FIG. 17.

At 2108, a third etch is performed into the backside of the substrate toform an inter-pixel isolation trench, where the inter-pixel isolationtrench comprises a pair of segments, and where the photodetector, theintra-pixel isolation trench, and absorption enhancement opening aresandwiched between the segments. See, for example, FIG. 18.

At 2110, a backside dielectric layer is formed covering the backside ofthe substrate, and further filling the inter-pixel and intra-pixelisolation trenches and the absorption enhancement opening, to form aCBSI structure and inter-pixel trench isolation structure. See, forexample, FIG. 19. A portion of the CBSI structure in the intra-pixelisolation trench (i.e., an intra-pixel trench isolation structure)prevents radiation from passing between pixel sensors and reflectsradiation leaving the photodetector back to the photodetector.Similarly, a portion of the CBSI structure in the absorption enhancementopening (i.e., an absorption enhancement structure) reflects radiationleaving the photodetector back to the photodetector. The CBSI structuremay, for example, achieve reflectance by TIR and has the effect ofreducing cross talk, increasing absorption, and increasing quantumefficiency.

At 2112, color filters and micro lenses are formed on the backsidedielectric layer. See, for example, FIG. 20.

While the block diagram 2100 of FIG. 21 is illustrated and describedherein as a series of acts or events, it will be appreciated that theillustrated ordering of such acts or events is not to be interpreted ina limiting sense. For example, some acts may occur in different ordersand/or concurrently with other acts or events apart from thoseillustrated and/or described herein. Further, not all illustrated actsmay be required to implement one or more aspects or embodiments of thedescription herein, and one or more of the acts depicted herein may becarried out in one or more separate acts and/or phases.

With reference to FIGS. 22-28 a series of cross-sectional views2200-2800 of some alternative embodiments of a method for forming animage sensor comprising CBSI structures is provided in which the imagesensor further comprises a composite grid. Further, inter-pixel trenchisolation structures are formed after CBSI structures. Thecross-sectional views 2200-2800 illustrate the method using the imagesensor of FIG. 3A but may also be used to form the image sensor in anyone of FIGS. 3B, 6A, 6B, 10, 14A, and 14B.

As illustrated by the cross-sectional view 2200 of FIG. 22, pixelsensors 104 are formed on a frontside 106 f of a semiconductor substrate106 and, in some embodiments, the semiconductor substrate 106 isthinned. Further, a backside 106 b of the semiconductor substrate 106 ispatterned to form absorption enhancement openings 1602 and intra-pixelisolation trenches 1702. The absorption enhancement openings 1602 andthe intra-pixel isolation trenches 1702 may, for example, be asdescribed with regard to FIGS. 16 and 17 and/or may, for example, beformed as described with regard to FIGS. 16 and 17.

As illustrated by the cross-sectional view 2300 of FIG. 23, a CBSI layer2302 is formed covering the backside 106 b of the semiconductorsubstrate 106, and further filling the absorption enhancement openings1602 (see FIG. 22) and the intra-pixel isolation trenches 1702 (see FIG.22). The CBSI layer 2302 may, for example, be or comprise silicon oxideand/or some other suitable dielectric(s). Further, the CBSI layer 2302may, for example, have a refractive index less than that of thesemiconductor substrate 106. In some embodiments, the CBSI layer 2302 isformed by CVD, PVD, thermal oxidation, some other suitable depositionprocess(es), or any combination of the foregoing.

As illustrated by the cross-sectional view 2400 of FIG. 24, aplanarization is performed into the CBSI layer 2302 (see FIG. 23) untilthe semiconductor substrate 106 is reached to form CBSI structures 102.Further, the backside 106 b of the semiconductor substrate 106 ispatterned to form an inter-pixel isolation trench 1802. The inter-pixelisolation trench 1802 separates the pixel sensors 104 from each otherand may, for example, be formed as described with regard to FIG. 18. Theplanarization may, for example, be performed by a CMP or some othersuitable planarization process.

As illustrated by the cross-sectional view 2500 of FIG. 25, a firstbackside liner 318, a second backside liner 320, and a first backsidedielectric layer 314 a are formed. The first and second backside liners318, 320 line the inter-pixel isolation trench 1802 (see FIG. 24), andthe first backside dielectric layer 314 a fills the inter-pixelisolation trench 1802 over the first and second backside liners 318,320. The first backside liner 318, the second backside liner 320, andthe first backside dielectric layer 314 a collectively define aninter-pixel trench isolation structure 116 in the inter-pixel isolationtrench 1802. The first backside liner 318 and/or the first backsidedielectric layer 314 a may be or comprise, for example, silicon oxideand/or some other suitable dielectric(s). In some embodiments, the firstbackside liner 318 and the first backside dielectric layer 314 a are thesame material. The second backside liner 320 may be or comprise, forexample, a high k dielectric and/or some other suitable dielectric(s).

The first and second backside liners 318, 320 may, for example, beformed by CVD, PVD, thermal oxidation, some other suitable depositionprocess(es), or any combination of the foregoing. The first backsidedielectric layer 314 a may, for example, be formed by depositing thefirst backside dielectric layer 314 a and subsequently perform aplanarization into the first backside dielectric layer 314 a. Theplanarization may, for example, be performed by a CMP or some othersuitable planarization process.

In alternative embodiments, the formation of the CBSI layer 2302 at FIG.23 and the planarization at FIG. 24 are omitted. In such alternativeembodiments, the first backside liner 318 and the second backside liner320 line the absorption enhancement openings 1602 (see FIG. 22) and theintra-pixel isolation trenches 1702 (see FIG. 22). Further, the firstbackside dielectric layer 314 a fills the absorption enhancementopenings 1602 and the intra-pixel isolation trenches 1702 over the firstbackside liner 318 and the second backside liner 320. Accordingly, theCBSI structures 102 may, for example, be defined by the first backsideliner 318, the second backside liner 320, and the first backsidedielectric layer 314 a in alternative embodiments.

As illustrated by the cross-sectional view 2600 of FIG. 26, a metallayer 312, a second backside dielectric layer 314 b, and a hard masklayer 316 (collectively a composite grid film) are formed stacked on thefirst backside dielectric layer 314 a.

As illustrated by the cross-sectional view 2700 of FIG. 27, the metallayer 312, the second backside dielectric layer 314 b, and the hard masklayer 316 are patterned to define a composite grid 302 and to form colorfilter openings 2702 overlying the pixel sensors 104. In someembodiments, the patterning is performed by an etching process or someother suitable patterning process. The etching process may, for example,comprise: 1) forming a mask 2704 on the hard mask layer 316; 2) applyingone or more etchants 2706 with the mask 2704 in place; and 3) strippingthe mask 2704.

As illustrated by the cross-sectional view 2800 of FIG. 28, a compositegrid liner 314 c is formed covering the hard mask layer 316 and liningthe color filter openings 2702 (see FIG. 27). Further, color filters 120are formed filling the color filter openings 2702 over the compositegrid liner 314 c and microlenses 122 are formed on the color filters120. The composite grid liner 314 c may be or comprise, for example,silicon oxide and/or some other suitable dielectric(s).

Although the cross-sectional views 2200-2800 shown in FIGS. 22-28 aredescribed with reference to a method, it will be appreciated that thestructures shown in FIGS. 22-28 are not limited to the method but rathermay stand alone separate of the method. Although FIGS. 22-28 aredescribed as a series of acts, it will be appreciated that these actsare not limiting in that the order of the acts can be altered in otherembodiments, and the methods disclosed are also applicable to otherstructures. In other embodiments, some acts that are illustrated and/ordescribed may be omitted in whole or in part.

With reference to FIG. 29, a block diagram 2900 of some embodiments ofthe method of FIGS. 22-28 is provided.

At 2902, a substrate and a photodetector are provided, where thephotodetector is in the substrate. See, for example, FIG. 22.

At 2904, a first etch is performed into a backside of the substrate todefine an absorption enhancement opening with slanted sidewalls, wherethe opening overlies the photodetector. See, for example, FIG. 22.

At 2906, a second etch is performed into the backside of the substrateto define an intra-pixel isolation trench, where the intra-pixelisolation trench borders the absorption enhancement opening. See, forexample, FIG. 22.

At 2908, a first dielectric layer is formed covering the backside of thesubstrate, and further filling the absorption enhancement opening andthe intra-pixel isolation trench. See, for example, FIG. 23.

At 2910, a planarization is performed into the first dielectric layeruntil the substrate to form a CBSI structure in the absorptionenhancement opening and the intra-pixel isolation trench. See, forexample, FIG. 24. The CBSI structure serves as a reflector to confineradiation to the substrate using, for example, TIR. By confiningradiation, the CBSI structure reduces cross talk, increases absorption,and increases quantum efficiency.

At 2912, a third etch is performed into the backside of the substrate toform an inter-pixel isolation trench, where the inter-pixel isolationtrench comprises a pair of segments, and where the photodetector and theCBSI structure are sandwiched between the segments. See, for example,FIG. 24.

At 2914, a second dielectric layer is deposited covering the backside ofthe substrate, and further filling the inter-pixel isolation trench.See, for example, FIG. 25.

At 2916, a planarization is performed into the second dielectric layerto flatten an upper or top surface of the second dielectric layer and toform an inter-pixel trench isolation structure in the inter-pixelisolation trench. See, for example, FIG. 25.

At 2918, a composite grid, color filters, and micro lenses are formed onthe second dielectric layer. See, for example, FIGS. 26-28.

While the block diagram 2900 of FIG. 29 is illustrated and describedherein as a series of acts or events, it will be appreciated that theillustrated ordering of such acts or events is not to be interpreted ina limiting sense. For example, some acts may occur in different ordersand/or concurrently with other acts or events apart from thoseillustrated and/or described herein. Further, not all illustrated actsmay be required to implement one or more aspects or embodiments of thedescription herein, and one or more of the acts depicted herein may becarried out in one or more separate acts and/or phases.

With reference to FIGS. 30-46, a series of cross-sectional views3000-4600 of some embodiments of a method for forming a 3D BSI imagesensor comprising CBSI structures is provided. The cross-sectional views3000-4600 illustrate the method using the 3D BSI image sensor of FIG. 15but may also be used to form alternative embodiments of the 3D BSI imagesensor with embodiments of the CBSI structures in any one of thepreceding figures.

As illustrated by the cross-sectional view 3000 of FIG. 30, a firstintegrated chip 1502 and a second integrated chip 1504 are bondedtogether frontside to frontside. The first and second integrated chips1502, 1504 may, for example, be as described with regard to FIG. 15. Thebonding may, for example, be performed by fusion bonding, hybridbonding, or some other suitable bonding process.

As illustrated by the cross-sectional view 3100 of FIG. 31, a firstsubstrate 106 of the first integrated chip 1502 is thinned to reduce athickness T_(ss) of the first substrate 106. The thickness T_(ss) may,for example, be reduced to about 2.5 micrometers or some other suitablethickness. Also illustrated, a sacrificial dielectric layer 3102 isformed on a backside of the first substrate 106. The sacrificialdielectric layer 3102 may, for example, be or comprise silicon oxideand/or some other suitable dielectric(s).

As illustrated by the cross-sectional view 3200 of FIG. 32, a backsideof the first substrate 106 is patterned to form absorption enhancementopenings 1602 and intra-pixel isolation trenches 1702 overlying thephotodetectors 108, and to further form an inter-pixel isolation trench1802 separating the photodetectors 108. The patterning may, for example,be performed according to the acts illustrated and described with regardto FIGS. 16-18. Also, the sacrificial dielectric layer 3102 (see FIG.31) is removed by, for example, an etching process, a cleaning process,or some other suitable removal process.

As illustrated by the cross-sectional view 3300 of FIG. 33, a firstbackside liner 318, a pair of second backside liners 320 a, 320 b, athird backside liner 1540, and a metal layer 3302 are formed stacked onthe backside of the first substrate 106, filling the absorptionenhancement openings 1602 (see FIG. 32), the intra-pixel isolationtrenches 1702 (see FIG. 32), and the inter-pixel isolation trench 1802(see FIG. 32). This forms CBSI structures 102 in the absorptionenhancement openings 1602 and the intra-pixel isolation trenches 1702,and further forms an inter-pixel trench isolation structure 116 in theinter-pixel isolation trench 1802 and a first metal grid 1542 in theinter-pixel isolation trench 1802. Note that because of the scale of theabsorption enhancement openings 1602 and the intra-pixel isolationtrenches 1702, it was impractical to show the first backside liner 318,the pair of second backside liners 320 a, 320 b, and third backsideliner 1540 in the absorption enhancement openings 1602 and theintra-pixel isolation trenches 1702. Hence, the hashing of the CBSIstructures 102 has been varied and represents the first backside liner318, one or both of the second backside liners 320 a, 320 b, the thirdbackside liner 1540, or any combination of the foregoing.

In alternative embodiments, the absorption enhancement openings 1602 andthe intra-pixel isolation trenches 1702 are filled with a dielectricmaterial before forming the first backside liner 318. For example, thedielectric material may be deposited and planarized before forming thefirst backside liner 318. An example of this is show at FIGS. 23 and 24.

As illustrated by the cross-sectional view 3400 of FIG. 34, an etch backis performed into the metal layer 3302 to recess a top surface of themetal layer 3302 to below a top surface of the third backside liner1540. The etch back may, for example, also thin the third backside liner1540. Additionally, after the etch back, a cap layer 1544 is formedcovering the third backside liner 1540 and the first metal grid 1542. Insome embodiments, formation of the cap layer 1544 comprises depositingthe cap layer 1544 and subsequently performing a planarization into thecap layer. Other processes are, however, amenable.

As illustrated by the cross-sectional view 3500 of FIG. 35, a patterningprocess is performed on the backside of the first substrate 106 to forma TSV opening 3502. The patterning process may, for example, beperformed by a photolithography/etching process or some other suitablepatterning process. Also, a pair of TSV liners 1552, 1554 are formedcovering the cap layer 1544 and lining the TSV opening 3502.

As illustrated by the cross-sectional view 3600 of FIG. 36, a patterningprocess is performed on the backside of the first substrate 106 toextend the TSV opening 3502 to a second interconnect structure 1530 ofthe second integrated chip 1504. The patterning process may, forexample, be performed by a photolithography/etching process or someother suitable patterning process.

As illustrated by the cross-sectional view 3700 of FIG. 37, the TSVopening 3502 (see FIG. 36) is filled by a conductive material to form aTSV 1550 in the TSV opening 3502. A process for filling the TSV opening3502 may, for example, comprise depositing a conductive layer fillingthe TSV opening 3502 and performing a planarization into the conductivelayer. Additionally, an etch stop layer 1546 is formed covering the TSV1550, the cap layer 1544, and the TSV liners 1552, 1554.

As illustrated by the cross-sectional view 3800 of FIG. 38, a patterningprocess is performed on the backside of the first substrate 106 to forma first pad opening 3802. The patterning process may, for example, beperformed by a photolithography/etching process or some other suitablepatterning process. Also, a pad dielectric liner 1526 is formed coveringthe etch stop layer 1546 and lining the first pad opening 3802.

As illustrated by the cross-sectional view 3900 of FIG. 39, a patterningprocess is performed on the backside of the first substrate 106 toextend the first pad opening 3802 to a first interconnect structure 1506of the first integrated chip 1502. The patterning process may, forexample, be performed by a photolithography/etching process or someother suitable patterning process. Also, a pad layer 3902 is formedcovering the pad dielectric liner 1526 and lining the first pad opening3802 (as extended) over the pad dielectric liner 1526.

As illustrated by the cross-sectional view 4000 of FIG. 40, the padlayer 3902 is patterned into a pad structure 1522. The patterning may,for example, also thin the pad dielectric liner 1526 and/or may, forexample, be performed by a photolithography/etching process or someother suitable patterning process. Also, a pad dielectric layer 1528 isformed filling the first pad opening 3802 (see FIG. 39) over the padstructure 1522.

As illustrated by the cross-sectional view 4100 of FIG. 41, the paddielectric layer 1528 is patterned to partially remove portions of thepad dielectric layer 1528 to sides of the pad structure 1522. Thepatterning may, for example, be a performed by aphotolithography/etching process or some other suitable patterningprocess.

As illustrated by the cross-sectional view 4200 of FIG. 42, the paddielectric layer 1528 and the pad dielectric liner 1526 are recesseduntil localized to the first pad opening 3802 (see FIG. 39). Therecessing may, for example, be performed by a planarization and/or anetch back. The planarization may, for example, be performed by a CMPand/or some other suitable planarization process. The patterning at FIG.41 may, for example, reduce CMP loading when the recessing is at leastpartially performed by a CMP.

As illustrated by the cross-sectional view 4300 of FIG. 43, a patterningprocess is performed on the backside of the first substrate 106 to formground openings 4202 exposing the first substrate 106. The patterningmay, for example, be performed by a photolithography/etching process orsome other suitable patterning process.

As illustrated by the cross-sectional view 4400 of FIG. 44, a metallayer 312 is formed over the etch stop layer 1546, the pad dielectriclayer 1528, and the pad dielectric liner 1526, and further filling theground openings 4202 (see FIG. 43). Also, a backside dielectric layer314 b and a hard mask layer 316 are formed stacked over the metal layer312.

As illustrated by the cross-sectional view 4500 of FIG. 45, the metallayer 312, the backside dielectric layer 314 b, and the hard mask layer316 are patterned to form a composite grid 302 defining color filteropenings 2702. The patterning may, for example, be performed by aphotolithography/etching process or some other suitable patterningprocess. Also, a composite grid liner 314 c is formed lining thecomposite grid 302.

As illustrated by the cross-sectional view 4600 of FIG. 46, the paddielectric layer 1528 and the composite grid liner 314 c are patternedto form a second pad opening 1524. The patterning may, for example, beperformed by a photolithography/etching process or some other suitablepatterning process. Further, color filters 120 are formed in the colorfilter openings 2702 (see FIG. 45) and microlenses 122 are formed on thecolor filters 120.

Although the cross-sectional views 3000-4600 shown in FIGS. 30-46 aredescribed with reference to a method, it will be appreciated that thestructures shown in FIGS. 30-46 are not limited to the method but rathermay stand alone separate of the method. Although FIGS. 30-46 aredescribed as a series of acts, it will be appreciated that these actsare not limiting in that the order of the acts can be altered in otherembodiments, and the methods disclosed are also applicable to otherstructures. In other embodiments, some acts that are illustrated and/ordescribed may be omitted in whole or in part.

In some embodiments, the present application provides an image sensorincluding: a substrate; a first trench isolation structure extendinginto a backside of the substrate to a first depth and including a pairof first trench isolation segments; a photodetector in the substrate,between and bordering the first trench isolation segments; a secondtrench isolation structure between the first trench isolation segments,wherein the second trench isolation structure extends into the backsideof the substrate to a second depth less than the first depth andincludes a pair of second trench isolation segments; and an absorptionenhancement structure overlying the photodetector and between the secondtrench isolation segments, wherein the absorption enhancement structureis recessed into the backside of the substrate. In some embodiments, theabsorption enhancement structure adjoins the second trench isolationstructure, wherein a bottom surface of the absorption enhancementstructure is flat and extends from one of the second trench isolationsegments to another one of the second trench isolation segments. In someembodiments, the absorption enhancement structure has slanted sidewalls.In some embodiments, the absorption enhancement structure is spaced fromthe second trench isolation structure and has a triangular profile. Insome embodiments, the absorption enhancement structure overlaps with thesecond trench isolation structure and has a downward protrusion with atriangular profile. In some embodiments, the absorption enhancementstructure and the second trench isolation structure include a dielectricmaterial with a refractive index less than that of the substrate. Insome embodiments, the second trench isolation structure has top layoutthat is a square ring shaped. In some embodiments, the second trenchisolation structure has a top layout that is cross shaped. In someembodiments, the absorption enhancement structure has a top layout thatis square or diamond shaped.

In some embodiments, the present application provides an image sensorincluding: a substrate; a trench isolation structure extending into abackside surface of the substrate to a first depth and including a pairof trench isolation segments; a photodetector in the substrate, betweenand next to the trench isolation segments; and a dielectric structure onthe backside surface of the substrate, wherein the dielectric structureprotrudes into the backside surface to a second depth less than thefirst depth, and wherein the dielectric structure has slanted sidewallsthat overlie the photodetector and slant from the backside surface to amidpoint between the backside surface and the second depth. In someembodiments, a width of the dielectric structure decreases from thebackside surface of the substrate to the midpoint and is substantiallyuniform from the midpoint to the second depth. In some embodiments, abottom profile of the dielectric structure is M shaped. In someembodiments, the slanted sidewalls meet at the midpoint. In someembodiments, the dielectric structure has a ring-shaped portionsurrounding the slanted sidewalls and overlying the photodetector,wherein the ring-shaped portion has the second depth.

In some embodiments, the present application provides a method forforming an image sensor, the method including: forming a photodetectorin a substrate; performing a first etch into a backside of the substrateto form an absorption enhancement opening (AEO) overlying thephotodetector and having slanted sidewalls; performing a second etchinto the backside of the substrate to form a first isolation trench(FIT) bordering the AEO; performing a third etch into the backside ofthe substrate to form a second isolation trench (SIT) extending into thebackside of the substrate to a greater depth than the FIT, and whereinthe SIT includes opposing segments between which the photodetector, theAEO, and the FIT are sandwiched; and filling the AEO, the FIT, and theSIT with a dielectric material. In some embodiments, the AEO has atriangular profile, and wherein the FIT has a top layout that is squarering shaped. In some embodiments, the second etch is performed into thesubstrate through the AEO, such that the AEO and the FIT overlap. Insome embodiments, the AEO and the SIT have top layouts that are squareand/or diamond shaped. In some embodiments, the absorption enhancementopening has an isosceles-trapezoid profile upon completion of the firstetch. In some embodiments, the filling includes: depositing a dielectriclayer in the AEO, the FIT, and the SIT, and further covering thebackside of the substrate, wherein the dielectric layer includes thedielectric material; and performing a planarization into the dielectriclayer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An image sensor comprising: a substrate; a pixelsensor comprising a photodetector in the substrate; a first trenchisolation structure comprising a pair of first trench isolationsegments, wherein the first trench isolation segments are respectivelyon opposite sides of the pixel sensor at a boundary of the pixel sensorand extend into a backside of the substrate to a first depth; a secondtrench isolation structure extending into the backside of the substrateto a second depth less than the first depth between the first trenchisolation segments; and an absorption enhancement structure overlyingthe photodetector between the first trench isolation segments, whereinthe absorption enhancement structure is recessed into the backside ofthe substrate and has a sidewall directly contacting the second trenchisolation structure.
 2. The image sensor according to claim 1, whereinthe sidewall of the absorption enhancement structure is slanted anddirectly contacts a sidewall of the second trench isolation structure ata third depth in the backside of the substrate that is less than thesecond depth.
 3. The image sensor according to claim 1, wherein thesecond trench isolation structure has a pair of second trench isolationsegments extending into the backside of the substrate to the seconddepth and laterally between the first trench isolation segments.
 4. Theimage sensor according to claim 3, wherein the absorption enhancementstructure has a surface extending from one of the second trenchisolation segments to another one of the second trench isolationsegments, and wherein the surface has a planar profile.
 5. The imagesensor according to claim 1, wherein the absorption enhancementstructure has a saw-toothed profile with multiple teeth culminating atpoints in the backside of the substrate, and wherein the points are at athird depth less than the second depth in the backside.
 6. The imagesensor according to claim 1, wherein the second trench isolationstructure has only one segment extending to the second depth between thefirst trench isolation segments when viewed in cross-section.
 7. Theimage sensor according to claim 1, wherein the second trench isolationstructure is at a width-wise center of the photodetector.
 8. An imagesensor comprising: a substrate; a first trench isolation structurecomprising a pair of first trench isolation segments that extend into abackside of the substrate to a first depth; a photodetector in thesubstrate, between the first trench isolation segments; a second trenchisolation structure comprising a pair of second trench isolationsegments that extend into the backside of the substrate to a seconddepth less than the first depth between the first trench isolationsegments; and an absorption enhancement structure overlying thephotodetector and extending into the backside of the substrate betweenthe second trench isolation segments; wherein the substrate extendscontinuously and linearly from one of the first trench isolationssegments to another one of the first trench isolations segments at athird depth in the backside of the substrate that is between and offsetfrom the first and second depths.
 9. The image sensor according to claim8, wherein the absorption enhancement structure extends into thebackside of the substrate to a fourth depth less than the second depthbetween the second trench isolation segments.
 10. The image sensoraccording to claim 9, wherein the substrate extends continuously andlinearly from one of the second trench isolations segments to anotherone of the second trench isolations segments at a fifth depth in thebackside of the substrate that is between and offset from the second andfourth depths.
 11. The image sensor according to claim 8, furthercomprising: a color filter overlying the photodetector on the backsideof the substrate and having a pair of sidewalls respectively on oppositesides of the color filter, wherein the first trench isolation segmentsrespectively underlie the sidewalls of the color filter.
 12. The imagesensor according to claim 8, further comprising: a micro lens overlyingthe photodetector on the backside of the substrate and having a pair ofbottom corners respectively on opposite sides of the micro lens, whereinthe first trench isolation segments respectively underlie the bottomcorners.
 13. The image sensor according to claim 8, wherein thesubstrate extends continuously and linearly from the one of the firsttrench isolations segments to the another one of the first trenchisolations segments in a direction parallel with a top surface of thesubstrate.
 14. The image sensor according to claim 8, wherein theabsorption enhancement structure is spaced from the second trenchisolation segments.
 15. An image sensor comprising: a substrate; a firsttrench isolation structure comprising a pair of first trench isolationsegments extending into a backside of the substrate; a photodetector inthe substrate, between the first trench isolation segments; a secondtrench isolation structure extending into the backside of the substrateto a lesser depth than the first trench isolation segments between thefirst trench isolation segments; and an absorption enhancement structureextending into the backside of the substrate to a lesser depth than thesecond trench isolation structure; wherein the photodetector is an onlyphotodetector between the first trench isolation segments when viewed incross section.
 16. The image sensor according to claim 15, wherein thesecond trench isolation structure comprises a pair of second trenchisolation segments, and wherein the absorption enhancement structure isbetween the second trench isolation segments.
 17. The image sensoraccording to claim 16, wherein the absorption enhancement structureculminates in a point between the second trench isolation segments. 18.The image sensor according to claim 15, wherein the absorptionenhancement structure has a pair of slanted sidewalls respectively onopposite sides of the photodetector, and wherein the second trenchisolation structure is between and contact the slanted sidewalls. 19.The image sensor according to claim 15, further comprising: a metal gridcomprising a pair of metal segments respectively and directly over thefirst trench isolation segments on the backside of the substrate; anddielectric material extending continuously and linearly from one of themetal segments to another one of the metal segments at an elevationoffset from a bottom surface of the metal grid.
 20. The image sensoraccording to claim 15, further comprising: a color filter overlying thephotodetector on the backside of the substrate and having a pair ofsidewalls respectively on opposite sides of the photodetector, whereinthe second trench isolation structure is laterally between thesidewalls.